It is known to produce bis(n-alkyl cyclopentadienyl) metallocenes by reaction of alkyl cyclopentadienyl lithenides with Group IV metal tetrahalides.
It is also known to react a cyclopentadienyl Grignard in ether with allyl bromide or tert.butyl bromide. See, e.g., Metallocenes, Wiley-VCH, Vol. 1, 469-47 (1998), citing Riemschneider, R. Z., Naturforsch. (1963) 18:641-645.